My tuttle is not opening one eye

Question
HI,

i bought two small turtles of nearly 3 cms long. i have provided every thing they need like uv bulb, heater , big acquarium and good food.
but one of my turtle among those two is not opening one eye.And its not active like the other one.
can i know what is the problem with that small cute turtle.

Answer
I need to know specifically how you have them set up:  exact size of tank, type of filter, brand of UVB bulb (not UV; it needs to be a special reptile bulb), exact water and basking temperatures, and complete diet.  Telling me you've provided everything they need doesn't tell me what I need to know, because if you've relied on pet shop advice you were probably given the wrong information.  The eye problem could be any number of things, but with the lethargy it's likely there's either a problem with your setup or the turtle wasn't very healthy to begin with.  If I have specific information, I can give you better advice.  How long have you have the turtles and what species are they?  Where did you get them?